Geometric-electronic shielding effect: Steering the glycerol electrooxidation on PdBi catalysts toward selective value-added organic products

Electrocatalytic oxidation of glycerol for value-added chemicals is a superior strategy to utilize the excess glycerol produced in the biodiesel industry. Pd is one of the few active catalysts for alkaline glycerol oxidation reaction (GOR); however, glycerol inevitably dissociates and converts to carbon dioxide on the Pd surface, which results in its low total Faradaic efficiency (FE) for high-value-added products. Herein, a series of Pd/C and Pd₁₀Bi_x/C catalysts were synthesized to investigate the GOR pathway. The Pd₁₀Bi₃/C catalyst with optimal Bi content achieved an excellent GOR mass activity of 7.5±0.2 A mg_Pd⁻¹ and an outstanding total FE of 90 %±3 %, which are much higher than those values on Pd/C (1.2±0.2 A mg_Pd⁻¹ for mass activity and 63 %±4 % for total FE). Combined results of in-situ attenuated total reflection surface enhanced infrared absorption spectroscopy and density functional theory calculations show that Bi suppresses the dissociation of glycerol through the “shielding effect” of Bi to the adjacent Pd sites, which weakens the adsorption strength of GOR intermediates on those sites. This work provides a new insight into the GOR mechanism and puts forward a valid strategy for the rational design of catalysts to enable the transformation of glycerol into high-value-added products.